3-D Air Flow in a Toroidal Natural Convection Loop

Heat transfer characteristics of air flows in concentric toroidal annular tubes filled with porous media were numerically investigated. The toroidal annulus is constant walls temperature where the outer wall temperature is lower than the inlet temperature. The numerical methodology was based on the finite difference approximation method. The computations were performed for vertical and horizontal toroidal ring, four toroidal length and four radius ratios cases for a modified Rayleigh number range (10≤Ra≤5000). The inner tube radius ranged from 0. 15 to 0. 4 m with the radius ratios Rr 0. 333, 0. 555, 0. 777 and 0. 888 and a length of 0. 05, 0. 1, 0. 15 and 0. 2m. The local Nusselt number in the angular direction for both walls and the average Nusselt number in concentric toroidal annular tubes were obtained. In addition the isothermal lines and the streamlines were investigated. The results show that The vertical toroidal loop is more suitable than the horizontal one because the heat transfer is less so the temperature values will be higher and remain high for a longer time which is required in such devices The best design of such devices is to take L=0. 05 with inner radius of 0. 15 m and to use it at δ =0 (vertical)